FIG. 1 is a cross-sectional view of a conventional capacitive touch device, in which a sensor layer 10 is coated with an adhesive 12 thereon, for a protective layer 14 to adhere thereto to prevent users' direct contact with the sensor layer 10. The sensor layer 10 is constructed from a multi-layer printed circuit board, and has X-axis and Y-axis sensor traces for generating a capacitance variation responsive to an object touching thereon. The lower surface of the printed circuit board is for circuit wiring and mounting of devices, such as a detector 16. The detector 16 is to detect the capacitance variation taking place at the sensor layer 10. When a finger 18 touches the protective layer 14, the capacitance variation that the detector 16 detects from the X-axis and Y-axis sensor traces will have a distribution over the X-axis and Y-axis as shown in FIG. 2. The equivalent capacitance established by the human finger 18 and the sensor layer 10 increases the capacitance detected by the detector 16, so the position of the finger 18 can be identified by referring to the capacitance variation. The foregoing conventional approach, however, can only work with the capacitance variation caused by human fingers or conductors sized in a particular range, and is not useful to the cases where nonconductors are involved. As another defect, the conventional approach is limited by the thickness of the protective layer 14 adhered onto the sensor layer 10. If the protective layer 14 is excessively thick, detection of the detector 16 to the sensor layer 10 in terms of capacitance variation will be degraded.
Therefore, it is desired a capacitive touch device capable of distinguishing between conductor and nonconductor.